CoatingsPro Magazine

MAY 2015

CoatingsPro offers an in-depth look at coatings based on case studies, successful business operation, new products, industry news, and the safe and profitable use of coatings and equipment.

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Page 52 of 92

52 MAY 2015 COATINGSPROMAG.COM falling behind, CMT had no choice but to remove the mess with shovels and buckets. Tey piled the grit on tarps outside the tank and let the owner dispose of it, as per the agreement. "It took us several hours," said CMT project superintendent (now technical specialist) Lloyd Prontaut. "Once all that was done, we put up the scafold and set up our Aqua Miser ultra- high pressure [UHP] blast machine. But that night, a storm came through and along with it, freezing temperatures. In the morning, everything was covered with glaze. You can't spray a 38,000 psi [262 MPa] UHP gun in icy conditions. It was strictly a safety concern. Tat gun pushes back pretty hard, and you certainly wouldn't want to slip. We had to call of the job the next two days." Te storm passed, and the CMT crew was eager to make up lost time. But amazingly, the same polyurea coating that fell away in some places adhered tenaciously in others. To maximize production, the UHP nozzle man found it best to hold the tip one to two inches (2.5–5 cm) from the polyurea. At that distance, the triple rotating on the Aqua Miser (by Caroline Equipment & Supply Company) head formed a pattern only about ¼ inch (0.6 cm) wide, so going was slow. Since the polyurea measured up to one-inch thick (2.5 cm) in places, holding the tip at a slight angle helped the UHP blast get under the coating and lift it more quickly. Te tightly clinging polyurea comprised about one half of the tank's 2,826 square foot (263 m²) interior surface. Te crew shoveled blast debris into buckets, which were hand carried to the tarps for disposal by the owner. Crummy Weather With the polyurea coating removed, CMT reviewed plans to abrasive blast to NACE No. 2/SSPC-SP-10: Near-White Metal Blast with a 3-mil (76 microns) anchor profle. Te storm had passed but left a cold snap in its wake. Te crummy weather wouldn't afect the blast, but it would afect the primer specifed, which ultimately afected how they would tackle the blast. "Te cold weather, in the 30° F [-1.1° C] range, became a challenge because we originally planned to use a Sherwin- Williams hold primer with a longer recoat window," Prontaut To the interior of the tank, the crew used ultrahigh pressure (UHP) water jetting and wet and dry abrasive blasting. They achieved a NACE No. 2/SSPC-SP-10: Near-White Metal Blast before getting ready for the coating. Then, after switching the primer due to the cold weather conditions, the crew spray-applied Sher win-Williams DURA-PL ATE 235 hold primer at 1–1.5 mils (25–38 microns) dry film thickness (DFT). Wastewater Tank Fix To the exterior, the crew pressure-washed the walls, spot-primed the welds and other areas with two different coatings, abraded existing coating, and brush- and roller-applied the aliphatic finish coat at 3–5 mils (76–127 microns) DFT. The topcoat for the interior was also spray-applied. It was Sher win- W i lli a m s SHERFLE X S , w h i c h w a s a p p li e d i n t w o p a s s e s w i t h crosshatch sweeps at an average of 60 mils (1,524 microns) total DFT.

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